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Chapter 4. Implementing the Interceptors Processing Logic

Abstract

Interceptors are straightforward to implement. The bulk of their processing logic is in the handleMessage() method. This method receives the message data and manipulates it as needed. Developers may also want to add some special logic to handle fault processing cases.
Figure 4.1, “Flow through an interceptor” shows the process flow through an interceptor.

Figure 4.1. Flow through an interceptor

Messages normally pass through an interceptor's handleMessage() method. In the event of a fault occurring at either the current interceptor or a later interceptor, the messages will pass through the interceptor's handleFault() method.
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Messages normally pass through an interceptor's handleMessage() method. In the event of a fault occurring at either the current interceptor or a later interceptor, the messages will pass through the interceptor's handleFault() method.
In normal message processing, only the handleMessage() method is called. The handleMessage() method is where the interceptor's message processing logic is placed.
If an error occurs in the handleMessage() method of the interceptor, or any subsequent interceptor in the interceptor chain, the handleFault() method is called. The handleFault() method is useful for cleaning up after an interceptor in the event of an error. It can also be used to alter the fault message.

4.1. Processing messages
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Overview
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In normal message processing, an interceptor's handleMessage() method is invoked. It receives that message data as a Message object. Along with the actual contents of the message, the Message object may contain a number of properties related to the message or the message processing state. The exact contents of the Message object depends on the interceptors preceding the current interceptor in the chain.

Getting the message contents
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The Message interface provides two methods that can be used in extracting the message contents:
  • public <T> T getContent(java.lang.Class<T>  format);
    The getContent() method returns the content of the message in an object of the specified class. If the contents are not available as an instance of the specified class, null is returned. The list of available content types is determined by the interceptor's location on the interceptor chain and the direction of the interceptor chain.
  • public Collection<Attachment> getAttachments();
    The getAttachments() method returns a Java Collection object containing any binary attachments associated with the message. The attachments are stored in org.apache.cxf.message.Attachment objects. Attachment objects provide methods for managing the binary data.
    Important
    Attachments are only available after the attachment processing interceptors have executed.

Determining the message's direction
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The direction of a message can be determined by querying the message exchange. The message exchange stores the inbound message and the outbound message in separate properties.[1]
The message exchange associated with a message is retrieved using the message's getExchange() method. As shown in Example 4.1, “Getting the message exchange”, getExchange() does not take any parameters and returns the message exchange as a org.apache.cxf.message.Exchange object.

Example 4.1. Getting the message exchange

Exchange getExchange();
The Exchange object has four methods, shown in Example 4.2, “Getting messages from a message exchange”, for getting the messages associated with an exchange. Each method will either return the message as a org.apache.cxf.Message object or it will return null if the message does not exist.

Example 4.2. Getting messages from a message exchange

Message getInMessage();
Message getInFaultMessage();
Message getOutMessage();
Message getOutFaultMessage();
Example 4.3, “Checking the direction of a message chain” shows code for determining if the current message is outbound. The method gets the message exchange and checks to see if the current message is the same as the exchange's outbound message. It also checks the current message against the exchanges outbound fault message to error messages on the outbound fault interceptor chain.

Example 4.3. Checking the direction of a message chain

public static boolean isOutbound()
{
   Exchange exchange = message.getExchange();
        return message != null
               && exchange != null
               && (message == exchange.getOutMessage()
                   || message == exchange.getOutFaultMessage());
}
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Example
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Example 4.4, “Example message processing method” shows code for an interceptor that processes zip compressed messages. It checks the direction of the message and then performs the appropriate actions.

Example 4.4. Example message processing method

import java.io.IOException;
import java.io.InputStream;
import java.util.zip.GZIPInputStream;

import org.apache.cxf.message.Message;
import org.apache.cxf.phase.AbstractPhaseInterceptor;
import org.apache.cxf.phase.Phase;

public class StreamInterceptor extends AbstractPhaseInterceptor<Message>
{

  ...
    
  public void handleMessage(Message message)
  {
  
        boolean isOutbound = false;
        isOutbound = message == message.getExchange().getOutMessage()
               || message == message.getExchange().getOutFaultMessage();

        if (!isOutbound)
        {
          try
          {
             InputStream is = message.getContent(InputStream.class);
             GZIPInputStream zipInput = new GZIPInputStream(is);
             message.setContent(InputStream.class, zipInput);
          }
          catch (IOException ioe)
          {
             ioe.printStackTrace();
           }
        }
         else
        {
         // zip the outbound message
        }
    }
  ...
}
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[1] It also stores inbound and outbound faults separately.
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